Photographic stripping films



3,282,698 PHOTOGRAPH-Ht! STRIPPING FILMS Johan Lodewijk Verelst, Konticlz, and Marcel Nicolas Vranclreu, Berellem-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel-Antwerp, Belgium, a Belgian company No Drawing. Filed Jan. 8, 1963, Ser. No. 250,028 Claims priority, application Netherlands, Jan. 15, 1962, 273,549 3 Claims. (Cl. 9683) This invention relates to a new photographic stripping film and to a process for making an etching resist by means of this stripping film. By means of this etching resist a metal printing plate can be made.

In many of the usual photographic stripping films the light-sensitive layer to be hardened image-wise is a gelatin bichromate layer. Such light-sensitive material involves, however, many disadvantages including a poor stability and necessitates long exposure times. Moreover, the obtained results are rather uncertain.

A photographic stripping film, the light-sensitive layer of which is a non-hardened gelatino-silver halide emulsion layer, does not present such disadvantages. For the greater part these photographic stripping films are mostly stripping films comprising a light-sensitive, non hardened gelatino-silver halide emulsion layer coated on a hydrophobic flexible membrane, which in its turn is releasably applied to a hydrophobic flexible backing or support.

The flexible support assures the dimensional stability during the exposure and the tanning development of the gelatino-silver halide emulsion layer. After pressing the tanning developed silver halide emulsion layer against the surface to be etched, the flexible support is removed. During and after this treatment, the hydrophobic membrane protects the tanning developed silver halide emulsion layer against deformation or tearing. The flexible support can easily be remove-d by stripping off, whereas the removal of the hydrophobic membrane, however, is a delicate operation which can easily lead to failures.

According to the US. Patent specification 2,650,878 the hydrophobic membrane is dissolved. However, by proceeding in such a way the control of the complete removal of the hydrophobic membrane is diflicult and, if not properly accomplished, can lead to irregularities during etching.

An improved process is described in the British Patent specification 835,170. According to the process of this patent specification, the nondissolved parts of the membrane are removed together with a layer composed of unhardened gelatin which is soluble in water of 30 to 40 C. and which is applied between the hydrophobic membrane and the lightsensitive silver halide emulsion layer. The penetration of enough water for dissolving this layer, however, requires rather much time and the dissolving itself requires water at a pretty high temperature, which afterwards gives rise to a considerable loss of time for cooling the printing rollers again, since these rollers must be cooled before the etching resist is allowed to dry. Morevover, the process according to said British patent specification causes easily failures, as during the tanning development, a local hardening of the gelatin layer, the so-called contact tanning, can occur under the most exposed parts of the silver halide emulsion layer by diffusing oxidation products of the used developer. Hence, the removal of the hydrophobic membrane on these areas is very diflicult to achieve. In order to solve this problem, a gelatin intermediate layer having a greater thickness can be applied, but the dimensional stability of the film is hereby decreased correspondingly.

Another process for removing the hydrophobic membrane from the tanning developed silver halide emulsion layer is described in the French Patent specification 1,281,283. According to this .process, the membrane is moistened with a mixture of liquids comprising a solvent for the membrane and a less volatile non-solvent. After this mixture of liquids has been partially evaporated, the hydrophobic membrane can be easily stripped oil as a coherent film. The removal of the hydrophobic membrane according to this process can still be improved by incorporating in this membrane plasticizers and by applying a very thin intermediate layer between the membrane and the light-sensitive silver halide emulsion layer. If these plasticizers are hydrophobic, residual parts of these substances can deposit, after the removal of the membrane, onto the most hardened tanning developed parts which are thus made less hydrophilic, whereby the penetration of the aqueous etching solution is locally decreased, so that a non-uniform etching may arise.

It has now been found that by applying a thin layer, mainly consisting of a hydrophilic colloid which is soluble in water of 30 to 40 C. and which cannot be hardened by aldehydes or quinones, between the subbed hydrophobic membrane and the silver halide emulsion layer of a stripping film, comprising in order: a hydrophobic flexible support, a stripping layer, a hydrophobic flexible membrane which is soluble in organic solvent, a subbing layer and a light-sensitive silver halide emulsion layer, on the one hand the contact tanning is eliminated, so that the hydrophobic membrane can be completely removed, and on the other hand the plasticizers can no longer deposit onto the tanning developed binding agent of the light-sensitive layer.

Hydrophilic colloids, which cannot be hardened with aldehydes or quinones and the physical properties of which are very well suitable for the obtention of the described layer, can be prepared by carrying out substitution reactions on the amino groups of gelatin as described in the Belgian Patent specifications 593,710 and 608,566. Particularly suitable compounds are the reaction products of gelatin and bromoacetic acid, pyromellitic dianhydride, p-carboxybenzly bromide, trirnellitic anhydride and o-methylisourea respectively. Some of the suitable hydrophilic colloids are even soluble in water of 25 C.

The thin non-hardenable layer according to the present invention is mostly applied from a solution of at least one of the non-hardenable compounds in suitable solvents or mixtures of solvents e.g. in water, in a mixture of water and a lower aliphatic alcohol occasionally containing alkaline substances etc. In this solution still other substances can occasionally be incorporated such as plasticizers, stabilizers, antihalation dyes, etc.

This solution is spread onto the hydrophobic membrane to which a subbing layer has been applied previously. The coating and drying temperatures are of no importance. Preferably, the thickness of the thin layer is kept very small (e.g. so that after drying the thickness is less than 4,11. and preferably varies from 0.3 to 1.5a). The influence of such a thin layer on the dimensional stability may be neglected. Indeed, for a given support the dimensional stability is determined by the forces which act in the back layers and in the front layers of the support, since these forces can occasionally cause a deformation of the support. Stronger forces at the front side of the material require a corresponding strengthening of the back layers in order to prevent curling of the material, this causing, however, an increase of the total amount of internal tensions exerted on the support, which in most cases is very disadvantageous. Since the thickness of the described intermediate layer consisting of a non-hardenable hydrophilic colloid amounts mostly only to 10% of the thickness of the light-sensitive emulsion layer, it is evident that the dimensional stability of a photographicstripping film according to the present invention is practically not influenced by said intermediate layer.

The hydrophobic support of a photographic stripping film according to the present invention can be manufactured from plastics such as cellulose diacetate, cellulose acetobutyrate, cellulose nitrate, cellulose triacetate, poly(ethylene terephthalate), poly(carbonate), etc. and its thickness amounts mostly from 50 to 200 1..

A suitable stripping layer may be composed of cellulose nitrate (from 6 to 9 parts) and ethyl cellulose (from 4 to 1 parts) if the [hydrophobic backing is made from a cellulose ester (such stripping layer is described in the US. patent specification 2,638,417). In the case the hydrophobic support is made from poly(ethylene terephthalate), such a suitable stripping layer can be composed of a copolymerization product of a diolefine and acrylonitrile or methacrylonitrile.

Appropriate layer-forming components for the manufacture of the hydrophobic flexible membrane of a photographic stripping film according to the present invention are plastics which are soluble in organic solvents such as cellulose nitrate, cellulose triacetate, cellulose propionate, cellulose acetobutyrate, cellulose acetopropionate, cellulose diacetate, a mixture of ethyl cellulose and cellulose nitrate, other single or mixed esters of carboxylic acids and cellulose, poly(amides), poly(carbonates), poly(esters), poly(vinyl chloride), poly(vinyl esters) and poly(vinyl acetals).

All types of emulsions, the binding agent of which mainly consists of a hydrophylic colloid which is hardenable with aldehydes or quinones and which is soluble in water of 30-40 C. when not hardened, may be used for preparing the light-sensitive silver halide emulsion layer.

In this description, only a very elementary specification has been given of the composition of a photographic stripping film according to the present invention. In addition to the mentioned essentially important layers, a photographic stripping film according to the present invention can still comprise other layers such as back layers, an anti-halation layer, a protective covering layer, etc.

The manufacture of the etch resists from-a photographic stripping film according to the invention can also be carriedout in different ways, although it is generally done as follows: image-wise exposure through a screen, tanning development, pressing against the surface to be etched, removal of the hydrophobic backing, removal of the flexible membrane e.g. according to a process as described in the French patent specification 1,281,283, washing away the unhardened parts and finally drying the obtained etching resist.

The following examples illustrate the present invention.

EXAMPLE 1 (a) Composition of the photographic stripping film Cellulose nitrate g 8 Ethylcellulose g 4 Methanol cm. 700 Acetone cm. 250 n-butanol cm. O

1 liter of this composition covers 1 sq. 111.

(3) A hydrophobic membrane, which is coated from the following coating solution:

Cellulose nitrate g 40 Tricresyl phosphate g 10 Diethylether g 200 Ethanol cm. 700 n-Butanol cm.

This solution is coated in such a way that after drying a layer is obtained of 14 g./sq. m.

(4) A subbing layer, which is applied from the following coating composition, so that 1 1. covers 45 sq. m.:

Gelatin g 2 Water 'g 17 Acetic acid cm. 1

methanol to 1000 emf.

(5) A thin layer according to the present invention and coated from the following composition:

Reaction product of gelatin and bromoacetic acid,

the preparation of which is described in the G. Belgian patent specification 608,566 20 Water Concentrated ammonium hydroxide 15 Methanol 800 This composition is coated in such a way, that after drying of the coated material, each sq. m. carries about 1 g. of non-hardenable colloid.

(6) A green-sensitized gelatino-silver chlorobromide emulsion layer completely free from hardeners.

(b) Manufacture of the etching resist The light-sensitive layer of this stripping film is first exposed through a continuous tone diapositive and then through a gravure screen. The exposed material is then immersed for 3 minutes in a solution of the following composition:

G. Sodium sulfate (anhydrous) 5 Sodium sulfite (anhydrous) 20 Pyrocatechol 6 Pyrogallol 8 1% solution of 6-nitrobenzimidazole in methanol 8 Water to 1000 cm.

Hereafter the developed material is immersed for 3 minutes into a solution consisting of:

Sodium carbonate (anhydrous) g Water to 1000 cm.

The developed material is then fixed for 5 minutes in a solution consisting of:

Water m. 800 Sodium thiosulfate g 200 Potassium metabisulfite g.. 25

Water to 1000 cm.

After washing and drying, the photogravure film is pressed with the emulsion side onto the wetted copper roller to be etched. After 1 minute the hydrophobic support is removed by stripping off.

The flexible membrane is contacted for 15 see. with the following mixture:

Cm. Acetone 400 Ethanol 500 Water 100 gether with the non-hardenable hydrophilic colloid, are washed away with water of about 50 C. Then the etch resist on the copper plate is dried.

The etching of the copper surface is carried out with aqueous ferric chloride (42 B.) according to the hardening pattern of the obtained etch resist.

EXAMPLE 2 Example 1 is repeated with a suchlike material, but of which the thin layer contains a non-hardenable hydrophilic colloid and is coated from the following composition:

Reaction product of gelatin and pyromellitic anhydride, the preparation of which has been described in the Belgian patent specification 593, 710 g 30 Water 'cm. 300 Ammonium hydroxide cm. 15 4% aqueous sodium hydroxide cm. 20 Methanol cm. 660

This composition is coated in such a way that after drying 1.2 g. of non-hardenable colloid is present per sq. m. of material.

EXAMPLE 3 566 g 25 Water cm. 200 Ammonium hydroxide cm. 15 4% aqueous sodium hydroxide cm. 60 Methanol cm. 660

This composition is coated in such a way, that after drying 1 g. of non-hardenable colloid is present per sq. m. of material.

To the silver halide emulsion, a sufficient amount of citric acid is added to neutralize the sodium hydroxide.

EXAMPLE 4 Example 1 is repeated with a suchlike material, but of which the thin layer contains a non-hardenable hydrophilic colloid and is coated from the following composition: Reaction product of gelatin and trimellitic anhydride,

the preparation of which is analoguou-s to the preparation described in the Belgian patent specification 593-710 'g 30 Water cm. 285 Ammonium hydroxide cm. 15 4% aqueous sodium hydroxide cm. 40 Water m. 660

This composition is coated in such a way, that after drying 1 g. of non-hardenable colloid is present per sq. m. of material.

EXAMPLE 5 Example 1 is repeated with a suchlike material, but of which the thin layer contains a non-hardenable hydrophilic colloid and is coated from the following com position:

Reaction product of gelatin and o-methylisourea, the preparation of which is described among others by A. W. Kenchiugton, :Biochem. J., 68, 1958, 459

g 30 Water cm. 2 85 Ammonium hydroxide cm. 20 4% aqueous sodium hydroxide crn. 35 Water cm. 660

This composition is coated in such a way, that after drying, 1 g. of non-hardenable colloid is present per sq. m. of material.

EXAMPLE 6 Example 1 is repeated with a suchlike material, but instead of the layers 1 and 2 the stripping film used for this example comprises the following layers:

(1) A polyethylene terephthalate support of a thickness of 100a, which is provided at its rear side with usual photographic subbing and antihalation layers.

(2) A stripping layer coated in such a way from the following composition, that 1 1. covers 36 sq. m. ofmaterial:

Copoly(butadiene/acrylonitrile) (60/40) g 25 Methylene chloride cm. 250 1,2-dich-loroet-hane cm. 550 Ethyl acetate cm. 225

This layer is dried at 80 C. We claim:

1. A photographic stripping film comprising in the indicated sequence (1) a hydrophobic flexible support, (2) a stripping layer, (3) a hydrophobic flexible membrane which is soluble in organic solvents, (4) a subbing layer,

(5) a thin layer predominantly consisting of gelatin having the amino groups thereof substituted and which is soluble in water of 3040 C., and (6) a light-sensitive silver halide emulsion layer, the binding agent of which predominantly consists of a hydrophilic colloid which is hardenable with a hardening agent selected from the group consisting of aldehydes and quinones and which in unhardened state is soluble in water of 3040 C.

2. A photographic stripping film comprising in the indicated sequence (1) a hydrophobic 'flexible support, (2) a stripping layer, (3) a hydrophobic flexible membrane which is soluble in organic solvents, (4) a subbing layer, (5) a thin layer of at most 4 thickness predominantly consisting of gelatin having the amino groups thereof substituted by reaction with a member of the group consisting of compounds having at least one acid anhydride group, at lea-st one active halogen atom, and lower alkylisourea and which is soluble in water of Sil -40 C., and ('6) a light-sensitive silver halide emulsion layer, the binding agent of which predominantly consists of a hydrophilic colloid which is hardenable with a hardening agent selected from the group consisting of aldehydes and quinones and which in unhardened state is soluble in water of 30-40 C.

3. A photographic stripping film comprising in the indicated sequence (1) a hydrophobic flexible support, (2)

V a stripping layer, (3) a hydrophobic flexible membrane References Cited by the Examiner UNITED STATES PATENTS 2,638,417 5/1953 White et al 9683 2,650,877 9/ 1953 'Boyer 9 6- 83 2,740,716 4/ 1956 Forman 96-83 2,993,790 6/ 1961 Grum-bine 9 683 3,011,890 12/1961 Gates et a1. 9 6-94 3,091,534- 5/1963 Nadeau et al. 96-83 3,118,766 1/1964 Roth 96-94 NORMAN G. TORCHIN, Primary Examiner.

A. D. RICCI, Assistant Examiner. 

1. A PHOTOGRAPHIC STRIPPING FILM COMPRISING IN THE INDICATED SEQUENCE (1) A HYDROPHOBIC FLEXIBLE SUPPORT, (2) A STRIPPING LAYER, (3) A HYDROPHOBIC FLEXIBLE MEMBRANE WHICH IS SOLUBLE IN ORGANIC SOLVENTS, (4) A SUBBING LAYER, (5) A THIN LAYER PREDOMINANTLY CONSISTING OF GELATIN HAVING THE AMINO GROUPS THEREOF SUBSTITUTED AND WHICH IS SOLUBLE IN WATER OF 30-40* C., AND (6) A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER, THE BINDING AGENT OF WHICH PREDOMINANTLY CONSISTS OF A HYDROPHILIC COLLOID WHICH IS HARDENABLE WITH A HARDENING AGENT SELECTED FROM THE GROUP CONSISTING OF ALDEHYDES AND QUINONES AND WHICH IS UNHARDENED STATE IS SOLUBLE IN WATER OF 30-40* C. 